It is well known in the automotive mirror art to provide a breakaway exterior rearview mirror assembly on a vehicle, wherein a head portion or movable portion of the mirror assembly may be pivotable via a pivot joint or breakaway joint assembly, such that the movable portion or head portion may be pivotable about a generally vertical pivot axis relative to a sail or base or fixed portion of the mirror assembly. The movable portion may be pivoted about the fixed portion and may be biased into one or more detent positions via a spring positioned generally around a post or support of the fixed portion. An upper end of the spring may engage a spring clip which may be generally fixedly positioned around the post of the fixed portion of the mirror assembly. Due to clearances between the spring clip and the movable portion, conventional mirror assemblies may have an undesirable amount of lateral displacement of an upper portion of the movable portion relative to the post of the fixed portion, commonly referred to as “head rock”.